Glucagonlike peptide-1 agonist stimulation of β-cell growth and differentiation:

Identification of 3-aminomethyl-1,2-dihydro-4-phenyl-1-isoquinolones: a new class of potent, selective, and orally active non-peptide dipeptidyl peptidase IV inhibitors that form a unique interaction with Lys554

The design, synthesis, and structure-activity relationships of a new class of potent and orally active non-peptide dipeptidyl peptidase IV (DPP-4) inhibitors, 3-aminomethyl-1,2-dihydro-4-phenyl-1-isoquinolones, are described. We hypothesized that the 4-phenyl group of the isoquinolone occupies the S1 pocket of the enzyme, the 3-aminomethyl group forms an electrostatic interaction with the S2 pocket, and the introduction of a hydrogen bond donor onto the 6- or 7-substituent provides interaction with the hydrophilic region of the enzyme. Based on this hypothesis, intensive research focused on developing new non-peptide DPP-4 inhibitors has been carried out. Among the compounds designed in this study, we identified 2-[(3-aminomethyl-2-(2-methylpropyl)-1-oxo-4-phenyl-1,2-dihydro-6-isoquinolinyl)oxy]acetamide (35a) as a potent, selective, and orally bioavailable DPP-4 inhibitor, which exhibited in vivo efficacy in diabetic model rats. Finally, X-ray crystallography of 35a in a complex with the enzyme validated our hypothesized binding mode and identified Lys554 as a new target-binding site available for DPP-4 inhibitors.

A perspective on pancreatic stem/progenitor cells

The prevalence of both type 1 and type 2 diabetes mellitus is increasing throughout the world along with the ensuant morbidity and early mortality because of premature microvascular and macrovascular disease. Current insulin and drug therapies control diabetes, but do not cure it. Cell-based therapies offer the possibilities of a permanent cure for diabetes. Recently, success in the transplantation of pancreatic islets in the livers of type 1 diabetics has afforded the opportunity for a potential cure. However, the severe shortage of donor islets for transplantation limits the usefulness of this therapy. One approach is to exploit the use of stem cells, either embryo-derived or adult tissue-derived, as substrates to create islet tissue suitable for transplantation. Cells isolated from embryo blastocysts and from adult pancreas, liver, and bone marrow can be expanded extensively in vitro and differentiated into islet-like clusters that produce insulin, and, in some instances, can achieve glycemic control when transplanted into streptozotocin-induced diabetic mice. It is, now, also possible to envision the direct systemic administration of stem cells that would home in on and regenerate injured islets, or to administer stem cell stimulators that would enhance endogenous pancreatic stem cells to expand and differentiate into functional, insulin-producing beta-cells. This perspective discusses the potential applications of cellular medicines, in the new discipline of regenerative medicine, to achieve a cure for diabetes.

Improvement of glucose tolerance in Zucker diabetic fatty rats by long-term treatment with the dipeptidyl peptidase inhibitor P32/98: comparison with and combination with rosiglitazone

AIM

The aim of this study was to investigate the effect of long-term treatment with the dipeptidyl peptidase inhibitor P32/98 and its combination with rosiglitazone on blood glucose control and islet of Langerhans histology in male Zucker diabetic fatty (ZDF) rats, when treatment begins before or after the development of overt diabetes.

METHODS

ZDF rats were treated with P32/98 from the age of 9, 12 or 15 weeks. Rosiglitazone maleate was given to a separate group from the age of 13 weeks. P32/98 was given to all of these rosiglitazone-treated rats from 16 weeks of age. Rosiglitazone maleate was also given from 16 weeks of age to half the rats that were given P32/98 from 9 weeks of age. The compounds were given by oral gavage until the rats were 14 weeks old and then in the diet. The experiment was terminated at the age of 20-21 weeks. Blood glucose, plasma insulin and oral glucose tolerance were measured at intervals; islet histology was assessed terminally.

RESULTS

P32/98 improved glucose tolerance after both single and multiple doses when treatment started at 9 weeks of age, also after the third week of treatment when treatment began at 12 or 15 weeks of age. P32/98 reduced daytime blood glucose when treatment began at 12 weeks. Treatment with rosiglitazone increased food intake and body weight, and after 2 weeks, reduced daytime blood glucose, water intake and the area under the glucose tolerance curve. A single dose of P32/98 markedly improved glucose tolerance in rosiglitazone-treated rats. When treatment had begun at 9 weeks of age, P32/98 stimulated insulin secretion in some glucose tolerance tests. Neither P32/98 nor rosiglitazone affected pancreatic insulin content, nor did they have clear effects on islet histology.

CONCLUSION

P32/98 elicited a sustained improvement in glucose tolerance in both prediabetic and diabetic ZDF rats. The effects of P32/98 on glucose and insulin were similar to those of rosiglitazone, and in contrast to rosiglitazone, P32/98 did not increase food intake or body weight. However, neither compound was especially effective at improving diabetes in ZDF rats when treatment began at 9, 12 or 15 (P32/98) or 13 (rosiglitazone) weeks of age.

Incretin Mimetics as Emerging Treatments for Type 2 Diabetes

OBJECTIVE:

To review the physiology, pharmacology, and clinical efficacy of glucagon-like peptide (GLP-1) and the incretin mimetics exenatide and liraglutide in clinical studies.

DATA SOURCES:

Primary literature obtained via MEDLINE (1966–April 2004) and International Pharmaceutical Abstracts (1970–April 2004) searches; abstracts obtained from meeting sources and manufacturers.

STUDY SELECTION AND DATA EXTRACTION:

All English-language studies and abstracts evaluating GLP-1, exenatide, and liraglutide in the treatment of patients with type 2 diabetes were reviewed. Data from animal studies were also included if human data were not available. Primary and review articles related to the physiology, development, and evaluation of GLP-1s were reviewed.

DATA SYNTHESIS:

GLP-1, exenatide (exendin-4, AC2993), and liraglutide (NN2211) are incretin mimetics that have been shown in human studies to be an effective treatment to improve glycemic control in patients with type 2 diabetes. Mechanisms by which these compounds improve glycemic control include enhancing glucose-dependent pancreatic secretion of insulin in response to nutrient intake, inhibiting glucagon secretion, delaying gastric emptying, and promoting early satiety. GLP-1 has been shown to promote pancreatic progenitor cell differentiation and improve β-cell function and lifespan. Reported adverse effects of exenatide and liraglutide include nausea, vomiting, and transient headache, as well as increased risk of hypoglycemia when used with sulfonylureas.

CONCLUSIONS:

Clinical studies show that GLP-1, exenatide, and liraglutide improve glycemic control for patients with type 2 diabetes through unique mechanisms not available with current pharmaceutical products. Ongoing Phase III studies will help to further position these compounds as treatment options for patients with type 2 diabetes.

Expression of pancreatic duodenal hoemobox-1 in pancreatic islet neogenesis after surgical wrapping in rats

BACKGROUND

Surgical wrapping (SW) of the pancreas causes islet neogenesis in rodents. Pancreatic duodenal hoemobox-1 (PDX-1) is one of the transcriptional factors needed by pancreatic stem cells to develop a mature pancreas. The purpose of this study was to determine whether islet neogenesis arises from ductal cells and whether PDX-1 is involved in this process.

METHODS

SW consisted of nonocclusive wrapping of the pancreas in rats. The wrapped pancreas was then harvested, insulin content was measured, and immunohistochemical analysis for insulin, cytokeratin, and PDX-1 was performed.

RESULTS

The endocrine area of the wrapped pancreas significantly increased after SW. Double immunostaining identified cells positive for both insulin and cytokeratin in or along the epithelial cell lining of the ductal structures and in the centroacinar cells. PDX-1-positive cells were detected in both control islets and islets examined after SW, but these cells were observed in the exocrine area only after SW. Double staining also showed that cells positive for PDX-1 but negative for insulin were present in the exocrine area 1 day after SW and that cells positive for both PDX-1 and insulin had developed 3 days after SW.

CONCLUSIONS

In the process of adult islet neogenesis after SW, cells in the acini and ductal structures developed into PDX-1-expressing cells, supposedly progenitor cells, which in turn became insulin-producing cells and thus might be the origin of small islets.

1-[[(3-hydroxy-1-adamantyl)amino]acetyl]-2-cyano-(S)-pyrrolidine: a potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitor with antihyperglycemic properties

Dipeptidyl peptidase IV (DPP-IV) inhibition has the potential to become a valuable therapy for type 2 diabetes. The synthesis and structure-activity relationship of a new DPP-IV inhibitor class, N-substituted-glycyl-2-cyanopyrrolidines, are described as well as the path that led from clinical development compound 1-[2-[5-cyanopyridin-2-yl)amino]ethylamino]acetyl-2-cyano-(S)-pyrrolidine (NVP-DPP728, 8c) to its follow-up, 1-[[(3-hydroxy-1-adamantyl) amino]acetyl]-2-cyano-(S)-pyrrolidine (NVP-LAF237, 12j). The pharmacological profile of 12j in obese Zucker fa/fa rats along with pharmacokinetic profile comparison of 8c and 12j in normal cynomolgus monkeys is discussed. The results suggest that 12j is a potent, stable, selective DPP-IV inhibitor possessing excellent oral bioavailability and potent antihyperglycemic activity with potential for once-a-day administration.

Stem/progenitor cells derived from adult tissues: potential for the treatment of diabetes mellitus

In view of the recent success in pancreatic islet transplantation, interest in treating diabetes by the delivery of insulin-producing beta-cells has been renewed. Because differentiated pancreatic beta-cells cannot be expanded significantly in vitro, beta-cell stem or progenitor cells are seen as a potential source for the preparation of transplantable insulin-producing tissue. In addition to embryonic stem (ES) cells, several potential adult islet/beta-cell progenitors, derived from pancreas, liver, and bone marrow, are being studied. To date, none of the candidate cells has been fully characterized or is clinically applicable, but pancreatic physiology makes the existence of one or more types of adult islet stem cells very likely. It also seems possible that pluripotential stem cells, derived from the bone marrow, contribute to adult islet neogenesis. In future studies, more stringent criteria should be met to clonally define adult islet/beta-cell progenitor cells. If this can be achieved, the utilization of these cells for the generation of insulin-producing beta-cells in vitro seems to be feasible in the near future.

Insulinotropic hormone glucagon-like peptide-1 differentiation of human pancreatic islet-derived progenitor cells into insulin-producing cells

Glucagon-like peptide-1 (GLP-1) is an intestinal incretin hormone, derived from the processing of proglucagon, that exerts insulinotropic actions on insulin-producing pancreatic islet beta-cells. Recently GLP-1 was shown to stimulate the growth and differentiation (neogenesis) of beta-cells and appears to do so by inducing the expression of the homeodomain protein IDX-1 (islet duodenum homeobox-1; also known as PDX-1, pancreatic and duodenal homeobox gene; and as IPF-1, insulin promoter factor), which is required for pancreas development and the expression of beta-cell-specific genes. Earlier we identified multipotential progenitor cells in the islet and ducts of the pancreas, termed nestin-positive islet-derived progenitor cells (NIPs). Here we report the expression of functional GLP-1 receptors on NIPs and that GLP-1 stimulates the differentiation of NIPs into insulin-producing cells. Furthermore, confluent NIP cultures express the proglucagon gene and secrete GLP-1. These findings suggest a model of islet development in which pancreatic progenitor cells express both GLP-1 receptors and proglucagon with the formation of GLP-1. Locally produced GLP-1 may act as an autocrine/paracrine developmental morphogen on receptors on NIPs, resulting in the activation of IDX-1 and the expression of the proinsulin gene conferring a beta-cell phenotype. GLP-1 may be an important morphogen both for the embryonic development of the pancreas and for the neogenesis of beta-cells in the islets of the adult pancreas.

1-[2-[(5-Cyanopyridin-2-yl)amino]ethylamino]acetyl-2-(S)-pyrrolidinecarbonitrile: a potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitor with antihyperglycemic properties

Dipeptidyl peptidase IV (DPP-IV) inhibition has the potential to become a valuable therapy for type 2 diabetes. We report the first use of solid-phase synthesis in the discovery of a new DPP-IV inhibitor class and a solution-phase synthesis that is practical up to the multikilogram scale. One compound, NVP-DPP728 (2), is profiled as a potent, selective, and short-acting DPP-IV inhibitor that has excellent oral bioavailability and potent antihyperglycemic activity.

Chronic inhibition of circulating dipeptidyl peptidase IV by FE 999011 delays the occurrence of diabetes in male zucker diabetic fatty rats

Acute suppression of dipeptidyl peptidase IV (DPP-IV) activity improves glucose tolerance in the Zucker fatty rat, a rodent model of impaired glucose tolerance, through stabilization of glucagon-like peptide (GLP)-1. This study describes the effects of a new and potent DPP-IV inhibitor, FE 999011, which is able to suppress plasma DPP-IV activity for 12 h after a single oral administration. In the Zucker fatty rat, FE 999011 dose-dependently attenuated glucose excursion during an oral glucose tolerance test and increased GLP-1 (7-36) release in response to intraduodenal glucose. Chronic treatment with FE 999011 (10 mg/kg, twice a day for 7 days) improved glucose tolerance, as suggested by a decrease in the insulin-to-glucose ratio. In the Zucker diabetic fatty (ZDF) rat, a rodent model of type 2 diabetes, chronic treatment with FE 999011 (10 mg/kg per os, once or twice a day) postponed the development of diabetes, with the twice-a-day treatment delaying the onset of hyperglycemia by 21 days. In addition, treatment with FE 999011 stabilized food and water intake to prediabetic levels and reduced hypertriglyceridemia while preventing the rise in circulating free fatty acids. At the end of treatment, basal plasma GLP-1 levels were increased, and pancreatic gene expression for GLP-1 receptor was significantly upregulated. This study demonstrates that DPP-IV inhibitors such as FE 999011 could be of clinical value to delay the progression from impaired glucose tolerance to type 2 diabetes.